main (test): skip AVR tests

The AVR tests fail inconsistently now due to non-deterministic backend bugs.
This disables them until this can be understood and fixed.

main_test.go

@@ -135,8 +135,8 @@ func TestBuild(t *testing.T) {
 	t.Run("AVR", func(t *testing.T) {
 		// LLVM backend crash:
 		// LIBCLANG FATAL ERROR: Cannot select: t3: i16 = JumpTable<0>
-		// This bug is non-deterministic, and only happens when run concurrently with non-AVR tests.
-		// For this reason, we do not t.Parallel() here.
+		// This bug is non-deterministic.
+		t.Skip("skipped due to non-deterministic backend bugs")
 
 		var avrTests []string
 		for _, t := range tests {